Effect of Fuel Composition on Emissions From a Low-Swirl Burner

2007 ◽  
Author(s):  
Daniel Sequera ◽  
Ajay K. Agrawal
Keyword(s):  
Gas Turbines ◽  
Bluff Body ◽  
Swirling Flow ◽  
Flame Temperature ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Recirculation Region ◽  
Fuel Composition ◽  
High Hydrogen ◽  
Flow Recirculation

Lean Premixed Combustion (LPM) is a widely used approach to effectively reduce pollutant emissions in advanced gas turbines. Most LPM combustion systems employ the swirling flow with a bluff body at the center to stabilize the flame. The flow recirculation region established downstream of the bluff-body brings combustion products in contact with fresh reactants to sustain the reactions. However, such systems are prone to combustion oscillations and flame flashback, especially if high hydrogen containing fuels are used. Low-Swirl Injector (LSI) is an innovative approach, whereby a freely propagating LPM flame is stabilized in a diverging flow field surrounded by a weakly-swirling flow. The LSI is devoid of the flow recirculation region in the reaction zone. In the present study, emissions measurements are reported for a LSI operated on mixtures of methane (CH4), hydrogen (H2), and carbon monoxide (CO) to simulate H2 synthetic gas produced by coal gasification. For a fixed adiabatic flame temperature and air flow rate, CH4 content of the fuel in atmospheric pressure experiments is varied from 100% to 50% (by volume) with the remainder of the fuel containing equal amounts of CO and H2. For each test case, the CO and nitric oxide (NOx) emissions are measured axially at the combustor center and radially at several axial locations. Results show that the LSI provides stable flame for a range of operating conditions and fuel mixtures. The emissions are relatively insensitive to the fuel composition within the operational range of the present experiments.

Impact of Fuel Composition on Blow Off and Flashback in Swirl Stabilized Lean Premixed Combustion

2013 ◽  
Author(s):  
Amin Akbari ◽  
Vincent McDonell ◽  
Scott Samuelsen
Keyword(s):  
Natural Gas ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Pollutant Emissions ◽  
Fuel Composition ◽  
Pure Hydrogen ◽  
Combustion Properties ◽  
Lean Premixed ◽  
The Impact

Co firing of natural gas with renewable fuels such as hydrogen can reduce greenhouse gas emissions, and meet other sustainability considerations. At the same time, adding hydrogen to natural gas alters combustion properties, such as burning speeds, heating values, flammability limits, and chemical characteristics. It is important to identify how combustion stability relates to fuel mixture composition in industrial gas turbines and burners and correlate such behavior to fuel properties or operating conditions. Ultimately, it is desired to predict and prevent operability issues when designing a fuel flexible gas turbine combustor. Fuel interchangeability is used to describe the ability of a substitute fuel composition to replace a baseline fuel without significantly altering performance and operation. Any substitute fuel, while maintaining the same heating load as the baseline fuel, must also provide stable combustion with low pollutant emissions. Interchangeability indices try to predict the impact of fuel composition on lean blowoff and flashback. Correlations for operability limits have been reported, though results are more consistent for blowoff compared to flashback. Yet, even for blowoff, some disagreement regarding fuel composition effects are evident. In the present work, promising correlations and parameters for lean blow off and flashback in a swirl stabilized lean premixed combustor are evaluated. Measurements are conducted for fuel compositions ranging from pure natural gas to pure hydrogen under different levels of preheat and air flow rates. The results are used to evaluate the ability of existing approaches to predict blowoff and flashback. The results show that, while a Damköhler number approach for blowoff is promising, important considerations are required in applying the method. For flashback, the quench constant parameter suggested for combustion induced vortex breakdown was applied and found to have limited success for predicting flashback in the present configuration.

scholarly journals Modelling of a Bluff-Body Stabilised Premixed Flames Close to Blow-Off

Computation ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 43
Author(s):  
Shokri Amzin ◽  
Mohd Fairus Mohd Yasin
Keyword(s):  
Bluff Body ◽  
Fluid Dynamic ◽  
Premixed Flames ◽  
Pollutant Emissions ◽  
Moment Closure ◽  
Recirculation Region ◽  
Scalar Dissipation ◽  
Average Error ◽  
Conditional Moment ◽  
Lean Premixed

As emission legislation becomes more stringent, the modelling of turbulent lean premixed combustion is becoming an essential tool for designing efficient and environmentally friendly combustion systems. However, to predict emissions, reliable predictive models are required. Among the promising methods capable of predicting pollutant emissions with a long chemical time scale, such as nitrogen oxides (NOx), is conditional moment closure (CMC). However, the practical application of this method to turbulent premixed flames depends on the precision of the conditional scalar dissipation rate,. In this study, an alternative closure for this term is implemented in the RANS-CMC method. The method is validated against the velocity, temperature, and gas composition measurements of lean premixed flames close to blow-off, within the limit of computational fluid dynamic (CFD) capability. Acceptable agreement is achieved between the predicted and measured values near the burner, with an average error of 15%. The model reproduces the flame characteristics; some discrepancies are found within the recirculation region due to significant turbulence intensity.

scholarly journals Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

1998 ◽  
Author(s):  
Rajiv Mongia ◽  
Robert Dibble ◽  
Jeff Lovett
Keyword(s):  
Power Spectrum ◽  
Mole Fraction ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

Towards Improved Boundary Layer Flashback Resistance of a 65 kW Gas Turbine With a Retrofittable Injector Concept

2018 ◽  
Author(s):  
Alireza Kalantari ◽  
Vincent McDonell ◽  
Scott Samuelsen ◽  
Shahram Farhangi ◽  
Don Ayers
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Elevated Pressure ◽  
Current Data ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Pollutant Emissions ◽  
Wall Region ◽  
Lean Premixed Combustion ◽  
High Hydrogen

Lean premixed combustion is extensively used in gas turbine industry to reduce pollutant emissions. However, combustion stability still remains as a primary challenge associated with high hydrogen content fuels. Flashback is a crucial concern for designing gas turbine combustors in terms of operability limits. The current experimental study addresses the boundary layer flashback of hydrogen-air premixed jet flames at gas turbine premixer conditions (i.e. elevated pressure and temperature). Flashback propensity of a commercially available injector, originally designed for natural gas, is studied at different operating conditions and corresponding measurements are presented. The pressure dependence of flashback propensity is consistent with previous studies. The previously developed flashback model is successfully applied to the current data, verifying its utilization for various test conditions/setups. In addition, the model is used to predict flashback propensity of the injector at the actual engine preheat temperature. The injector is then modified to increase boundary layer flashback resistance and the corresponding data are collected at the same operating conditions. To avoid the boundary layer flashback, the mixture is leaned out in the near-wall region, where the flame can potentially propagate upstream. The comparison of gathered data shows a clear improvement in flashback resistance. This improvement is further elaborated by numerically studying fuel/air mixing characteristics for the two injectors.

Numerical Simulation for the Preliminary Design of Fuel Flexible Stationary Gas Turbine Combustors Using Conventional and Alternative Fuels

2012 ◽  
Author(s):  
Washington Orlando Irrazabal Bohorquez ◽  
João Roberto Barbosa ◽  
Rob Johan Maria Bastiaans ◽  
Philip de Goey
Keyword(s):  
Numerical Simulation ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Alternative Fuels ◽  
High Efficiency ◽  
Numerical Study ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Gas Turbine Combustor ◽  
Primary Zone

Currently, high efficiency and low emissions are most important requisites for the design of modern gas turbines due to the strong environmental restrictions around the world. In the past years, alternative fuels have been considered for application in industrial gas turbines. Therefore, combustor performance, pollutant emissions and the ability to burn several fuels became of much concern and high priority has been given to the combustor design. This paper describes a methodology focused on the design of stationary gas turbines combustion chambers with the ability to efficiently burn conventional and alternative fuels. A simplified methodology is used for the calculations of the equilibrium temperature and chemical species in the primary zone of a gas turbine combustor. Direct fuel injection and diffusion flames, together with numerical methods like Newton-Raphson, LU Factorization and Lagrange Polynomials, are used for the calculations. Diesel, ethanol and methanol fuels were chosen for the numerical study. A computer code sequentially calculates the main geometry of the combustor. From the numerical simulation it is concluded that the basic gas turbine combustor geometry, for some operating conditions and burning diesel, ethanol or methanol, are of similar sizes, because the development of aerodynamic characteristics predominate over the thermochemical properties. It is worth to note that the type of fuel has a marked effect on the stability and combustion advancement in the combustor. This can be seen when the primary zone is analyzed under a steady-state operating condition. At full power, the pressure is 1.8 MPa and the temperature 1,000 K at the combustor inlet. Then, the equivalence ratios in the primary zone are 1.3933 (diesel), 1.4352 (ethanol) and 1.3977 (methanol) and the equilibrium temperatures for the same operating conditions are 2,809 K (diesel), 2,754 K (ethanol) and 2,702 K (methanol). This means that the combustor can reach similar flame stability conditions, whereas the combustion efficiency will require richer fuel/air mixtures of ethanol or methanol are burnt instead of diesel. Another important result from the numerical study is that the concentration of the main pollutants (CO, CO2, NO, NO2) is reduced when ethanol or methanol are burnt, in place of diesel.

Experimental Study of Flow Field Effect on Spray and Flame Structure in Swirl Stabilized Combustor

2019 ◽  
Author(s):  
Raju Murugan ◽  
Dhanalakshmi Sellan ◽  
Pankaj S. Kolhe
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Spatial Distribution ◽  
Gas Turbine ◽  
Liquid Fuel ◽  
Swirling Flow ◽  
Mixture Fraction ◽  
Flame Temperature ◽  
Operating Conditions ◽  
Fuel Gas

Abstract The spatial distribution of spray plays a key role in liquid fuel combustion, which dictates the local mixture fraction and the flame temperature distribution in gas turbine engines. The swirling flow creates further decomposition of the spray droplets in liquid fuel gas turbine engine, which increases the surface area of the droplets. Turbulent mixing due to the swirling flow is essential for preheating of unburned products and flame holding in the combustor. A lab-scale swirl stabilized liquid fuel combustor was designed and fabricated with the geometric swirl number (SN) of 1. Combustor flow geometry involves internal spray from flow blurring twin-fluid atomizer, surrounded by swirling airflow which is confined with co-flow air to provide full optical access. At constant spray operating conditions, the swirl Reynolds number (Re) is increased whereas co-flow velocity was maintained constant at 0.4 m/s. An experimental study was carried out to understand the effect of Reynolds number on the aerodynamic structure of airflow, the spatial distribution of spray structure and kerosene flame structures using Particle Image Velocimetry (PIV) and direct imaging. The experimental results show that the flow structure and spray spreads radially with the increase in swirl Reynolds number and the corresponding core spray height decreases, which were evident from flame images.

Boundary Layer Flashback Prediction for Turbulent Premixed Jet Flames: Comparison of Two Models

2019 ◽  
Author(s):  
Alireza Kalantari ◽  
Nicolas Auwaijan ◽  
Vincent McDonell
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Jet Flames ◽  
Turbulent Flame Speed ◽  
Turbulent Premixed

Abstract Lean-premixed combustion is commonly used in gas turbines to achieve low pollutant emissions, in particular nitrogen oxides. But use of hydrogen-rich fuels in premixed systems can potentially lead to flashback. Adding significant amounts of hydrogen to fuel mixtures substantially impacts the operating range of the combustor. Hence, to incorporate high hydrogen content fuels into gas turbine power generation systems, flashback limits need to be determined at relevant conditions. The present work compares two boundary layer flashback prediction methods developed for turbulent premixed jet flames. The Damköhler model was developed at University of California Irvine (UCI) and evaluated against flashback data from literature including actual engines. The second model was developed at Paul Scherrer Institut (PSI) using data obtained at gas turbine premixer conditions and is based on turbulent flame speed. Despite different overall approaches used, both models characterize flashback in terms of similar parameters. The Damköhler model takes into account the effect of thermal coupling and predicts flashback limits within a reasonable range. But the turbulent flame speed model provides a good agreement for a cooled burner, but shows less agreement for uncooled burner conditions. The impact of hydrogen addition (0 to 100% by volume) to methane or carbon monoxide is also investigated at different operating conditions and flashback prediction trends are consistent with the existing data at atmospheric pressure.

scholarly journals Approaches to the Prevaporized-Premixed Combustor Concept for Gas Turbines

1975 ◽  
Author(s):  
L. J. Spadaccini ◽  
E. J. Szetela
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Bluff Body ◽  
Porous Plate ◽  
Operating Conditions ◽  
Fuel Oil ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Operational Conditions ◽  
Lean Combustion

An experimental investigation was performed to evaluate a combustor concept which is applicable to gas turbine engines and is believed to offer valuable pollution control advantages relative to the conventional liquid-fuel-spray approach. It involves fuel prevaporization, premixing and lean combustion and may be applied to the design of combustors for aircraft, industrial or automotive powerplants. Two types of bluff-body flameholders, viz. porous-plate and drilled-plate, were evaluated for use as flame stabilizers within the combustor. Tests were conducted under sets of steady-state operational conditions corresponding, respectively, to applications in a low-pressure regenerative-cycle and high-pressure nonregenerative-cycle automobile gas turbine engines. The data acquired can be used to design gas turbine combustors having predicted performance characteristics which are better than those required to meet the most stringent automobile emissions regulations of the Federal “Clean Air Act.” Fuel prevaporization can be accomplished either externally, prior to admission into the engine airstream, or internally by the airstream itself. In support of the prevaporization concept, the feasibility of vaporizing No 2 fuel oil in a heat exchanger which is external to the engine was investigated. Tests conducted at representative operating conditions indicated that a deposit of 0.01 0-in. thickness was collected on the vaporizer wall after 50 hr of operation. A much shorter period of cleaning with hot air was sufficient to remove the deposit.

Fuel Flexibility Test Campaign on a 10 MW Class Gas Turbine Equipped With a Dry-Low-NOx Combustion System

2007 ◽  
Author(s):  
Stefano Cocchi ◽  
Michele Provenzale ◽  
Gianni Ceccherini
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Ratio ◽  
Flame Temperature ◽  
Nox Emission ◽  
Pollutant Emissions ◽  
Combustion System ◽  
Fuel Flow ◽  
Fuel Flexibility ◽  
Air Staging

An experimental test campaign, aimed to provide a preliminary assessment of the fuel flexibility of small power gas turbines equipped with Dry Low NOx (DLN) combustion systems, has been carried over a full-scale GE10 prototypical unit, located at the Nuovo-Pignone manufacturing site, in Florence. Such activity is a follow-up of a previous experimental campaign, performed on the same engine, but equipped with a diffusive combustion system. The engine is a single shaft, simple cycle gas turbine designed for power generation applications, rated for 11 MW electrical power and equipped with a DLN silos type combustor. One of the peculiar features of such combustion system is the presence of a device for primary combustion air staging, in order to control flame temperature. A variable composition gaseous fuel mixture has been obtained by mixing natural gas with CO2 up to about 30% vol. inerts concentration. Tests have been carried over without any modification of the default hardware configuration. Tests performed aimed to investigate both ignition limits and combustors’ performances, focusing on hot parts’ temperatures, pollutant emissions and combustion driven pressure oscillations. Results indicate that ignition is possible up to 20% vol. inerts concentration in the fuel, keeping the fuel flow during ignition at moderately low levels. Beyond 20% vol. inerts, ignition is still possible increasing fuel flow and adjusting primary air staging, but more tests are necessary to increase confidence in defining optimal and critical values. Speed ramps and load operation have been successfully tested up to 30% vol. inerts concentration. As far as speed ramps, the only issue evidenced has been risk of flameout, successfully abated by rescheduling combustion air staging. As far as load operation, the combustion system has proven to be almost insensitive to any inerts concentration tested (up to 30% vol.): the only parameter significantly affected by variation in CO2 concentration has been NOx emission. As a complementary activity, a simplified zero-dimensional model for predicting NOx emission has been developed, accounting for fuel dilution with CO2. The model is based on main turbine cycle and DLN combustion system controlling parameters (i.e., compressor pressure ratio, firing temperature, pilot fuel and primary air staging), and has been tuned achieving good agreement with data collected during the test campaign.

Modelling and Assessment of Compressor Faults on Marine Gas Turbines

2012 ◽  
Author(s):  
I. Roumeliotis ◽  
N. Aretakis ◽  
K. Mathioudakis ◽  
E. A. Yfantis
Keyword(s):  
Gas Turbines ◽  
Engine Performance ◽  
Performance Model ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Maximum Speed ◽  
Performance Modelling ◽  
Engine Operation ◽  
Marine Propulsion ◽  
And Performance

Any prime mover exhibits the effects of wear and tear over time, especially when operating in a hostile environment. Marine gas turbines operation in the hostile marine environment results in the degradation of their performance characteristics. A method for predicting the effects of common compressor degradation mechanisms on the engine operation and performance by exploiting the “zooming” feature of current performance modelling techniques is presented. Specifically a 0D engine performance model is coupled with a higher fidelity compressor model which is based on the “stage stacking” method. In this way the compressor faults can be simulated in a physical meaningful way and the overall engine performance and off design operation of a faulty engine can be predicted. The method is applied to the case of a twin shaft engine, a configuration that is commonly used for marine propulsion. In the case of marine propulsion the operating profile includes a large portion of off-design operation, thus in order to assess the engine’s faults effects, the engine operation should be examined with respect to the marine vessel’s operation. For this reason, the engine performance model is coupled to a marine vessel’s mission model that evaluates the prime mover’s operating conditions. In this way the effect of a faulty engine on vessels’ mission parameters like overall fuel consumption, maximum speed, pollutant emissions and mission duration can be quantified.

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